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Exceptional Generalized Geometry, Topological P-Branes and Wess-Zumino-Witten Terms

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Exceptional Generalized Geometry, Topological P-Branes and Wess-Zumino-Witten Terms Institut de Física d’Altes Energies (IFAE) High Energy Physics, Astrophysics and Cosmology Master’s Thesis Exceptional Generalized Geometry, Topological p-branes and Wess-Zumino-Witten Terms Author Supervisor Young Min Kim Roberto Rubio Núñez September 1, 2020 Abstract We study the interplay between the AKSZ construction of σ-models, the Hamilto- nian formalism in the language of symplectic dg-geometry, the encoding of dynamics and symmetries inside algebroid structures and the exceptional generalized geometric descrip- tion of supergravity theories. By utilizing the power of these higher geometric structure and constructions, we study the M5-brane Wess-Zumino term in the Green-Schwarz La- grangian of M5-brane coupled to the associated background flux in supergravity theories. We introduce the AKSZ construction and clarify its nature as a construction formalism for higher Chern-Simons theories, together with the Hamiltonian formalism nature of its geometric background. After embedding the E6 generalized tangent bundle into a symplectic dg-manifold, via AKSZ construction we obtain a 7-dimensional higher Chern- Simons theory, then from the boundary of the theory we obtain the Wess-Zumino term of the Green-Schwarz action functional for the Abelian M5-brane. We discuss and propose speculations on a three-fold coincidence between the D-branes in a transitive algebroid structure, well definedness of p-dimensional AKSZ σ-model boundary terms which can at the same time be seen as WZW terms of a p-dimensional Green Schwarz action functional, and the forcing of AKSZ σ-model boundary terms to lie in a Lagrangian submanifold. This is based on various observations made about the La- grangian submanifolds of the symplectic dg-manifolds in the corresponding Hamiltonian formalism and Dirac structures of higher Courant algebroids found in the literature. i Acknowledgement I am indebted to my thesis supervisor Ruberto Rubio for his guidance and numerous useful suggestions, and for providing the opportunity of my being introduced to the in- triguing fields of Poisson geometry, generalized geometry, mathematical physics, etc. It was an exciting and whole new experience and I wish I can continue to do research like this, in these fields, in the future. Many thanks to my family, my parents and my sister, for their support, without which the thesis would not have been possible, and for their being there. Even in this distance, from the westernmost of the largest continental area on Earth to the easternmost of it, I might have been hard to contact and I rarely say anything, but you are all in my heart. I will miss the serenity of Bellaterra and Sant Cugat del Vallès, especially the stillness of the cloister of the Monestir de Sant Cugat. I would also like to thank all the friendly people I encountered during the last year, even before the beginning of my master’s study. It is impossible for me to recall everyone, so I give thanks to God. ii Contents 1 Introduction 1 1.1 Motivations and Strategy ........................... 1 1.2 Outline ..................................... 4 1.3 Conventions and Nomenclature ........................ 5 2 Mathematical Preliminaries 6 2.1 Some Symplectic and Poisson Preliminaries ................. 6 2.2 Graded Algebraic Structures .......................... 7 2.3 Jet bundle approach to Classical Field Theory ................ 8 3 AKSZ construction, Chern-Weil theory and Symplectic dg-geometry 10 3.1 Differential Graded Geometry ......................... 10 3.2 Symplectic L1-algebroids ........................... 12 3.3 AKSZ σ-Models, and AKSZ actions as Chern-Simons functionals ..... 14 4 Properties of AKSZ σ-models and higher Courant algebroids 16 4.1 AKSZ σ-models with Boundary ........................ 16 4.2 Examples .................................... 17 4.2.1 Courant sigma model and ordinary 3d Chern-Simons theory .... 17 4.2.2 String sigma model in the case of exact Courant algebroids ..... 19 4.3 Exact Courant Algebroids and Variational Problems ............ 20 4.4 Higher Courant Algebroid, Variational Problems ............... 21 4.5 Lagrangian submanifolds and Current algebra ................ 22 5 Discussion: Bulk-Boundary duality and p-brane actions 24 5.1 Green-Schwarz action functional for p-branes ................. 25 5.2 AdS/CFT and CS-WZW correspondence ................... 25 6 Exceptional Generalized Geometry and 11D SUGRA 28 6.1 String Dualities preliminary .......................... 28 6.1.1 T-duality ................................ 28 6.1.2 S-duality ................................ 29 6.1.3 U-duality ................................ 30 6.2 Generalized Geometry ............................. 31 6.3 Exceptional Generalized Geometry ...................... 33 6.4 E6(6) Exceptional generalized geometry .................... 34 7 M2-brane action from AKSZ 36 iii iv CONTENTS 8 M5-brane Wess-Zumino term from AKSZ 38 8.1 Symplectic dg-geometry of E6 Exceptional Geometry ............ 38 8.2 σ-model and Wess-Zumino term ........................ 40 9 Discussion, Conclusions and Outlook 41 Appendix 44 Bibliography 46 Chapter 1 Introduction 1.1 Motivations and Strategy String theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. While string theory may or may not be the dreamt theory of everything, the understanding of string theory and its dualities has resulted in an deepening understanding of quantum field theories. The studies of AdS/CFT and AGT correspondence [1], Entanglement entropy, etc. cannot be isolated from the framework of string theory, and when studying gauge theories, con- formal theories, supersymmetries, the problems can more or less be mapped to some corresponding string or brane models. Hence a proper understanding of string theory is still relevant and important. After taking into account all the resonable consistency conditions, there are five pos- sible superstring theories: type I, type IIA, type IIB, and heterotic SO(32) and E8 × E8. In 1990s, various dualities between these superstring theories implied that all these are different formulations of a theory which is more fundamental. It is conjectured tobe the quantum theory of 11-dimensional supergravity (SUGRA). As a conjectured theory that unifies various string theories, M-theory still lacks a proper formulation. The stud- ies imply that higher structures play a crucial role in the description of these theories of extended objects. Formulations of SUGRA theories with string duality manifest results in their description in terms of (exceptional) generalized geometry. In the second quan- tization of the string, string field theory, the Hilbert space can carry higher homotopy algebras such as an L1 and A1 algebra. In Batalin-Vilkovisky formalism, the L1 algebra structure appears in every classical field theory [2]. Higher-degree form fields appearing in supergravity theories are connections on higher principal bundles. Topological p-brane σ-models can be constructed through AKSZ construction of field theories, which are based on the geometry of symplectic dg-manifolds. Nahm showed that 11 dimensions is the largest number of dimensions consistent with a single graviton with no higher-spin (greater than 2) particles, hence the maximal 11D SUGRA, along with the fact that the largest space-time dimension consistent with super- conformal symmetry is 6. The quantization of 11D SUGRA leads to a theory of 2-branes and 5-branes, and is precisely the aformentioned M-theory. Hence the 2- and 5-branes are called M-branes. The quantum field theory on the worldvolume of M5-branes isa6- dimensional (2,0) superconformal field theory, argued to be crucial to the understanding of deep physics and mathematics, for instance Khovanov homology, geometric Langlands duality and Montonen-Olive duality [3]. From this (2; 0)-theory one can obtain, for exam- 1 2 CHAPTER 1. INTRODUCTION ple, AGT correspondence and 3d-3d duality through topological twist or compactifiction. A proper formulation of the theory is more than desireable. However, the theory is far from being well understood. The Lagrangian description of several coincident M5-branes, being the classical limit of the (2; 0)-theory, is still unknown, and was argued to be non-existent. The argument for the non-existence is roughly as follows, M5-branes are where M2-brane ends, while the boundary of an M2-brane is a self-dual string, a 1-dimensional object. and sweeps a surface σ. The self-dual string is charged under certain group G, hence parallel transported along the surface σ. There is no reparametrization invariant notion of surface ordering, so the parallel transport of self-dual stringsR forces G to be Abelian, so that the 2-form connection B’s integral over the surface σ B is well defined. The obstruction that leads to this argument now seems to be circumventable, af- ter introducing 2-morphisms and 2-categories [4]. Consider a parallel transport of a 1-dimensional object subdivided into two pieces, with gi denoting the group action. The 0 0 0 0 original requirement that (g1g2)(g1g2) = (g1g1)(g2g2) can be expressed in a rather different way, that is 0 ⊗ 0 ◦ ⊗ 0 ◦ ⊗ 0 ◦ (g1 g2) (g1 g2) = (g1 g1) (g2 g2) this interchange law no longer forces the group action gi to be Abelian. Also successful M2-brane models have been constructed even if there are no continuous parameters in these models which suggests that there should be no Lagrangian description. Construction of a Lagrangian of coincident (hence non-Abelian) M5-branes is still a question worthy to ask. Now the problem is what the proper tools and frameworks for the study of M5- brane are. Here the notion of generalized geometry [5], Batalin Vilkovisky formalism and in particular AKSZ construction [6] come into mind. Inspired by various dualities in the string theory, in particular T-duality, the attempt to geometrize string theories and make the duality manifest have led to the formulation in terms of generalized geometry. Generalized geometry takes the metric and the 2-form gauge field, the 2-form B-field appearing in type II strings, in an equal footing and provides a natural framework for the study of string theory and supergravity.
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